1. Field of the Invention
The present invention relates to a method for driving a display panel.
2. Description of the Related Art
A display device having a plasma display panel mounted thereto as the display panel described above is described in JP-A-2000-155557, for example.
FIG. 1 shows a schematic construction of such a display device.
Referring to FIG. 1, a PDP 1 as the plasma display panel includes row electrodes Y1 to Yn and row electrodes X1 to Xn corresponding to rows (first to nth rows) of one screen, whereby each X and each Y form a pair. Column electrodes D1 to Dm are formed in such a fashion as to correspond columns (first to m-th columns) of one screen and to intersect these row electrodes. In this instance, a discharge cell as a capacitive light emitting device is formed at a point of intersection between one set of row electrode pair and one column electrode. An address driver 2 converts pixel data for each pixel based on an image signal to a pixel data pulse having a voltage value corresponding to a logic level of the pixel data and applies the pixel data pulse to the column electrodes D1 to Dm for each row. An X-row electrode driver 3 generates a reset pulse for initializing a residual wall charge quantity of each discharge cell and a sustain discharge pulse for sustaining a discharge light emission state of each light-on mode discharge cell to be later described and applies these pulses to the row electrodes X1 to Xn. A Y-row electrode driver 4 generates a reset pulse for initializing the residual wall charge quantity of each discharge cell and the sustain discharge pulse for sustaining the discharge light emission state of each light-on mode discharge cell and applies these pulses to the row electrodes Y1 to Yn in the same way as the X-row electrode driver 3. The Y-row electrode driver 4 further generates a priming pulse for re-forming charge particles generated inside the discharge cells and a scan pulse SP for causing each discharge cell to generate a quantity of charge corresponding to the pixel data pulse and for setting the light-on mode discharge cell or light-off mode discharge cells, and applies these pulses to the row electrodes Y1 to Yn.
FIG. 2 shows an internal construction of the X-row electrode driver 3 and the Y-row electrode driver 4. Incidentally, an electrode X1 in FIG. 2 represents an electrode of a j-th row among the electrodes X1 to Xn and an electrode Yj represents an electrode of a j-th row among the electrodes Y1 to Yn.
The X-row electrode driver 3 includes two power sources B1 and B2. The power source B1 outputs a voltage Vs1 (for example, 170 V) and the power source B2 outputs a voltage Vr1 (for example, 190 V). A positive terminal of the power source B1 is connected to a connection line 11 for the electrode Xj through a switching device S3 and its negative terminal is grounded. A switching device S4 is interposed between the connection line 11 and the earth. In addition, a series circuit including a switching device S1, a diode D1 and a coil L1 and a series circuit including a coil L2, a diode D2 and a switching device S2 are interposed between the connection line 11 and the earth through a capacitor C1 interposed on the earth side. Incidentally, the diode D1 is connected with its anode positioned on the side of the capacitor C1 and the diode D2, with its cathode positioned on the side of the capacitor C1. A positive terminal of the power source B2 is connected to the connection line 11 through a switching device S8 and a resistor R1 and its negative terminal is grounded. The Y-row electrode driver 4 includes four power sources B3 to B6. The power source B3 outputs the voltage Vs1 (for example, 170 V) and the power source B4 outputs the voltage Vr1 (for example, 190 V). The power source B5 outputs a voltage Voff (for example, 140 V) and the power source B6 outputs a voltage Vh (for example, 160 V, Vh>Voff). A positive terminal of the power source B3 is connected to a connection line 12 for a switching device 15 through a switching device S13 and its negative terminal is grounded. A switching device S14 is interposed between the connection line 12 and the earth. In addition, a series circuit including a switching device S11, a diode D3 and a coil L4 and a series circuit including a coil L4, a diode D4 and a switching device S12 are interposed between the connection line 12 and the earth through a capacitor C2 interposed on the earth side. Incidentally, the diode D3 is connected with its anode positioned on the side of the capacitor C2 and the diode D4, with its cathode positioned on the side of the capacitor C2. The connection line 12 is connected to a connection line 13 for a positive terminal of the power source B6 through a switching device S15. A positive terminal of the power source B4 is grounded and its negative terminal is connected to the connection line 13 through a switching device S16 and a resistor R2. A positive terminal of the power source B5 is connected to the connection line 13 through a switching device S17 and is negative terminal is grounded. The connection line 13 is connected to a connection line 14 for the electrode Yj through a switching device S21. A negative terminal of the power source B6 is connected to the connection line 14 through a switching device S22. A diode D5 is interposed between the connection lines 13 and 14 and a series circuit of a switching device S23 and a diode D6 is interposed between these connection lines 13 and 14, too. The diode D5 is connected with its anode positioned on the side of the connection line 14 and the diode D6, with its cathode positioned on the side of the connection line 14.
Here, a control circuit, not shown in the drawings, controls ON/OFF switching of the switching devices S1 to S4, S8, S11 to S17 and S21 to S23.
Incidentally, the power source B3, the switching devices S11 to S15, the coil L3, the coil L4, the diode D3, the diode D4 and the capacitor C2 constitute a sustain driver portion inside the Y-row electrode driver 4. The power source B4, the resistor R2 and the switching device S16 constitute a reset driver portion. The power source B5, the power source B6, the switching device S13, the switching device S17, the switching device S21, the switching device S22, diode D5 and D6 constitute a scan driver portion.
Next, operations under such a construction will be explained with reference to the timing chart of FIG. 3.
Driving of the PDP 1 is divided into a reset period, an address period and a sustain period as shown in FIG. 3.
First, in the reset period, the switching device S23 of the Y-row electrode driver 4 is turned ON. The switching device S23 remains ON during the reset period and the sustain period. At the same time, the switching device S8 of the X-row electrode driver 3 is turned ON and the switching device 16 of the Y-row electrode driver 4 is turned ON. Other switching devices are OFF. As the switching device S8 is turned ON, current flows from the positive terminal of the power source B2 into the electrode Xj through the switching device S8 and the resistor R1. As the switching device S16 is turned ON, current flows from the electrode Yj into the negative terminal of the power source B4 through the diode D5, the resistor R2 and the switching device S16. In this instance, the potential of the electrode Xj gradually rises depending on the time constant of the load capacitance C0 of the PDP 1 and the resistor R1 and a reset pulse RPx shown in FIG. 3 is generated. On the other hand, the potential of the electrode Yj gradually decrease depending on the time constant of the load capacitance C0 and the resistor R2 and a reset pulse RPy shown in FIG. 3 is generated. The reset pulse RPx is simultaneously applied to all the electrodes X1 to Xn and the reset pulse RPy is simultaneously applied to all the electrodes Y1 to Yn. Because of the simultaneous application of these reset pulses RPx and RPy, reset discharge is induced inside all the discharge cells of the PDP 1 and after this discharge finishes, wall charge of a predetermined quantity is uniformly formed in the dielectric layer of all the discharge cells. The switching devices S8 and S16 are turned OFF after the levels of the reset pulses RPx and RPy get into saturation but before the end of the reset period. At this point, the switching devices S4, S14 and S15 are turned ON and both of the electrodes Xj and Yj are grounded. Consequently, the reset pulses RPx and RPy disappear.
Next, in the address period, the switching devices S14 and S15 are turned OFF, the switching device S23 is turned OFF, the switching device S17 is turned ON and at the same time, the switching device S22 is turned ON. As the switching device S17 is turned ON, the power source B5 and the power source B6 enter a series connection state and a negative potential representing the difference between the voltages Vh and Voff occurs at the negative terminal of the power source B6 and is applied to the electrode Yj. In this address period, the address driver 2 converts pixel data for each pixel based on the image signal to each pixel data pulse DP1 to DPn having a voltage value corresponding to the logic level of the pixel data and serially applies it to the column electrodes D1 to Dm for each row. As shown in FIG. 3, the pixel data pulses DPj and DPj+1 are applied to the electrodes Yj and Yj+1. In the mean time, the Y-row electrode driver 4 serially applies the priming pulse PP of the positive voltage to the row electrodes Y1 to Yn and serially applies the scan pulse SP of the negative voltage in synchronism with the timing of the group of the pixel data pulses DP1 to DPn immediately after the application of each priming pulse PP. The explanation will be given on the electrode Yj. When the priming pulse PP is generated, the switching device S21 is turned ON and the switching device S22 is turned OFF. The switching device S17 remains OFF. Consequently, the potential Voff of the positive terminal of the power source B5 is applied as the priming pulse PP to the electrode Yj through the switching device S17 and then through the switching device S21. After the priming pulse PP is applied, the switching device S21 is turned OFF in synchronism with the application of the pixel data pulse DPj from the address driver 2 and the switching device S22 is turned ON. Accordingly, the negative potential representing the difference between the voltage Vh of the negative terminal of the power source B6 and Voff is applied as the scan pulse SP to the electrode Yj. The switching device S21 is turned ON in synchronism with the stop of the application of the pixel data pulse DPj from the address driver 2, the switching device S22 is turned OFF and the potential Voff of the positive terminal of the power source B5 is applied to the electrode Yj through the switching device S17 and then through the switching device S21. As for the electrode Yj+1, too, the priming pulse PP is thereafter applied in the same way as the electrode Yj and the scan pulse SP is applied in synchronism with the application of the pixel data pulse DPj+1 from the address driver 2. Among the discharge cells belonging to the row electrodes to which the scan pulse SP is applied, discharge occurs inside those discharge cells to which the pixel data pulse of the positive voltage is further applied simultaneously, and the majority of their wall discharge is lost. On the other hand, discharge does not occur in the discharge cells to which the scan pulse SP is applied but the pixel data pulse of the positive voltage is not applied and the wall charge remains as such. In this instance, the discharge cells in which the wall charge remains are light-on mode discharge cells and the discharge cells in which the wall charge disappears are light-off mode discharge cells. In the shift from the address period to the sustain period, the switching devices S17 and S21 are turned OFF. Instead, the switching devices S14 and S15 are turned ON. The ON state of the switching device S4 is kept.
Next, in the sustain period, the potential of the electrode Xj reaches the earth potential of about 0 V as the switching device S4 of the X-row electrode driver 3 is turned ON. Next, when the switching device S4 is turned OFF and the switching device S1 is turned ON, current reaches the electrode Xj due to the charge stored in the capacitor C1 through the coil L1, the diode D1 and the switching device S1 and charges the load capacitance C0 of the PDP 1. At this time, the potential of the electrode Xj gradually rises depending on the time constant of the coil L1 and the load capacitance C0. Next, the switching device S1 is turned OFF and the switching device S3 is turned ON. Consequently, the potential Vs1 of the positive terminal of the power source B1 is applied to the electrode Xj. The switching device S3 is thereafter turned OFF, the switching device S2 is turned ON and the current flows from the electrode Xj into the capacitor C1 due to the charge stored in the load capacitance C0 through the coil L2, the diode D2 and the switching device S2. At this time, the potential of the electrode j gradually decrease depending on the time constant of the coil L2 and the capacitor C1 as shown in FIG. 3. When the potential of the electrode Xj substantially reaches 0 V, the switching device S2 is turned OFF and the switching device S4 is turned ON. Due to such an operation, the X-row electrode driver 3 applies the sustain discharge pulse IPx of the positive voltage shown in FIG. 3 to the electrode Xj. At the ON time of the switching device S4 at which the sustain discharge pulse IPx disappears, the switching device S11 is simultaneously turned ON and the switching device S14 is turned OFF in the Y-row electrode driver 4. When the switching device S14 remains OFF, the potential of the electrode Yj is at the earth potential of about 0 V but when the switching device S14 is turned OFF and the switching device S11 is turned ON, the current reaches the electrode Yj due to the charge stored in the capacitor C2 through the coil L3, the diode D3, the switching device S11, the switching device S15, the switching device S13 and the diode D6 and charges the load capacitance C0 of the PDP 1. At this time, the potential of the electrode Yj gradually rises as shown in FIG. 3 depending on the time constant of the coil L3 and the load capacitance C0. Next, the switching device S11 is turned OFF and the switching device S13 is turned ON. Consequently, the potential VS1 of the positive terminal of the power source B3 is applied to the electrode Yj. Thereafter the switching device S13 is turned OFF, the switching device S12 is turned ON and the current flows from the electrode Yj into the capacitor C2 due to the charge stored in the load capacitance C0 through the diode D5, the switching device S15, the coil L4, the diode D4 and the switching device S12. At this time, the potential of the electrode Yj gradually decrease depending on the time constant of the coil L4 and the capacitor C2 as shown in FIG. 3. When the potential of the electrode Yj substantially reaches 0 V, the switching device S12 is turned OFF and the switching device S14 is turned ON. Due to such an operation, the Y-row electrode driver 4 applies the sustain discharge pulse IPy of the positive voltage shown in FIG. 3 to the electrode Yj.
Whenever the sustain discharge pulses IPx and IPy are applied in this way to the electrodes X1 to Xn and to the electrodes Y1 to Yn during the sustain period, the light-on mode discharge cells in which the wall charge remains repeat discharge light emission and keep the light emission state.
In driving shown in FIG. 3, however, the voltages of all the row electrodes Y sharply shift all at once to 0 V during the shift from the address period to the sustain period and noise occurs. In this instance, a large current resulting from such a noise flows in some cases into the driver IC and may invite the drop of IC's life.
The invention is completed to solve such problems and aims at providing a driving method of a display panel capable of improving durability of a driving device for driving the display panel.